1. Field of the Invention
The present invention relates to a slip control mechanism of a car.
2. Description of the Prior Art
There has previously been known a slip control system used as one of the electrical control systems of a car. The slip control system assures stability, maneuverability and high acceleration when starting a car and during running of a car. When driving wheels excessively slip due to excessive pressure applied to an accelerator by a driver, the performance of the car as regards, for example, stability and maneuverability, is reduced and acceleration also decreases. In the slip control system, acceleration of wheel rotation, speed or acceleration of the car, etc. are calculated by means of an electrical control mechanism based on signals from vehicle speed sensors connected to the wheels of the car, and if the excessive slip of the driving wheels is detected, the driving force transmitted to the driving wheels is restricted so as to restrict the excessive slip.
There are two ways of restricting the driving force transmitted to the driving wheels against the pressure applied to the accelerator by the driver. One way is to restrict the output of the engine, the other is to have the brake applied to the slipping wheel regardless of the operation by the driver. One of the slip control mechanisms which adopts the latter way is the control mechanism disclosed in Japanese Patent Laid-open Publication No. 60-179363. In this slip control mechanism, the hydraulic pressure of operating oil of an amplifying means or a hydraulic booster is used as the hydraulic pressure for braking so as to carry out the brake control for controlling the slip.
But, the above slip control mechanism includes the following problem. That is, when the slip control is stopped just after the hydraulic pressure of the operating oil of the hydraulic booster is supplied to the cylinders of the brakes of the driving wheels, the hydraulic pressure in the cylinders of the brakes of the driving wheels does not rapidly drop so that the release of the brakes is delayed, as the operation oil supplied to the cylinders of the brakes returns to a reservoir through orifices in the hydraulic booster. As a result, there is a decrease in the acceleration of the car.